The invention relates to a method for error correction in which descriptors contained in a transmission block combine code words for this transmission block having the same correction capability in subsets and describe the size of the subset and also the difference in the correction capability of the subset.
With regard to the packet-oriented transmission of data, in general bit errors occur in the case of fixed networks on account of an overload situation at network nodes and in the case of mobile channels as a result of atmospheric disturbances and multiple path propagations, the bit errors which are detected by error-detecting codes and result in entire packets being discarded. So-called Reliable Transport Protocols such as TCP use repeat mechanisms (Automatic Repeat Request method) in order to be able to reliably transport lost or discarded packets to the receiver in spite of faulty channels. However, this has associated with it a very considerable increase in transmission delay which nonetheless cannot be tolerated, particularly in the case of communication applications. Unreliable Transport Protocols, such as UDP for example, are therefore used here. While it is true that these cause no increase in the transmission delay, neither do they offer any form of mechanisms for compensating for packet losses. Intensive efforts have therefore been made for some time in the Audio Visual Transport Group (AVT) of the IETF to link methods for forward error correction (FEC) and packet-oriented transmission with Unreliable Transport Protocols. In this situation, a plurality of data packets are for example coded in one step and the z code words cwi, where 0<i<z, having the length N are arranged in such a way in a storage field that the code words form the rows or columns of a zxN or Nxz matrix. Columns or rows are then mapped to packets of a transport layer, for example RTP/UDP, and transmitted. In order to obtain a source-adaptive coding the code words cwi of a matrix can exhibit a different form of protection against errors or erasures.
If the correction capability of a code word cwi is designated as epi in the following, then a so-called error protection profile EPP describes the correction capability of the set of code words which are combined in a matrix EPP={ep0, ep1, . . . epz−1}. The error protection profiles of two successive matrixes or transmission blocks can be different, whether it be in order to adapt the error protection to the source or also to the channel. However, in order to be able to decode the code words of a transmission block at the receiver, the corresponding error protection profile EPP must be known or transmitted to the decoder. This requires reliable signaling. The signaling should be efficient in order to keep the additional overhead as small as possible. It would be very inefficient to transmit a sufficiently large number of fields in the header of each transmission packet for this purpose, and a transmission outside of the logical channel (out-of-band signaling) means an additional resource requirement. It is therefore better to use descriptors which combine code words of a transmission block having the same correction capability in a subset and describe the size of the subset as well as the difference in the correction capability of the previously initiated subset (differential description).